1. Field of the Invention
The present invention relates to an image forming apparatus using electrophotography and, more particularly, to a color misregistration detection technique in an image forming apparatus.
2. Description of the Related Art
An electrophotographic image forming apparatus called a tandem type is known. This tandem-type image forming apparatus is configured to sequentially transfer images from the image forming stations of the respective colors to the intermediate transfer belt and then transfer the images from the intermediate transfer belt to a printing medium at once.
In such an image forming apparatus, when the images are superimposed, color misregistration (positional shift) may occur due to the mechanical factors of the image forming stations of the respective colors. Especially in an arrangement in which each image forming station is provided with a photosensitive member and a scanner unit for scanning the photosensitive member, the positional relationship between the scanner unit and the photosensitive member changes between the colors. This impedes synchronization of laser beam scanning positions on the photosensitive members and causes color misregistration.
To correct the color misregistration, the image forming apparatus performs color misregistration correction control. In Japanese Patent Laid-Open No. 7-234612, position detection toner images of the respective colors are transferred from the photosensitive members to an image carrier such as an intermediate transfer belt. The positions of the respective color toner images relative to a reference color toner image are detected using a sensor, thereby performing the color misregistration correction control.
In the arrangement according to the related art, however, since the position detection toner images are formed on the image carrier, the toners are consumed, and a time is required for cleaning the toners, lowering the usability of the image forming apparatus.